The present invention relates to a fluid line status sensor system which can be used to determine whether fluid is flowing, contained, or absent in a pipe or vessel.
In a typical power plant, there are hundreds of fluid pipelines for conveying fluid (e.g., hot steam) through heat exchangers and to and from a turbine. Fluid which passes through these lines is, in many cases, at a temperature well above the ambient temperature of the environment in which the pipes are located.
Fluid pipe systems, such as those used in a typical power plant, may include flow status monitoring systems. Power plant monitoring and on-line diagnostic systems often require electronic verification of the flow status in various pipelines, such as drain lines or process fluid lines. As these lines can be valved in and out of the overall flow circuit, the flow in these lines may be intermittent.
It is beneficial to verify by independent signals whether contact closures associated with flow control devices, such as isolation valves or dump valves, have produced the state of flow expected. Generally, it is of interest to verify whether a large flow exists (e.g., a relatively large volume of fluid is flowing through the pipe), no flow exists, or a significant leakage flow exists (e.g., a relatively small volume of fluid is flowing from a leaky valve).
Diagnostic systems may employ sensors located at hundreds of locations about the fluid pipe systems. Such diagnostic systems can be extremely expensive. The total installed cost of sensors in such systems can be a significant portion of the overall system cost. Accordingly, it is beneficial to employ an inexpensive sensor at each of the sensing locations. Such inexpensive sensors may include thermocouples.
Some conventional systems employ several one-of-a-kind installations of thermocouple junction devices (hereafter referred to as thermocouples). Each installation having an arrangement of thermocouples mounted axially (with respect to the pipe) on a pipe surface across a valve or over a span where a significant thermal difference is developed during operation. However, this axial arrangement of thermocouples gives rise to several disadvantages. For example, several long lengths of wires are required to connect the axially arranged thermocouples with evaluation electronics. Additionally, engineering costs in determining locations for placing the thermocouples are relatively high in such conventional systems. Moreover, engineering costs for interpreting signals provided by several one-of-a-kind installations are relatively high. Furthermore, with the axially arranged thermocouples located to produce differential signals from two axial locations (e.g., on either side of an isolation valve), flow blockage occurring elsewhere (e.g., at the mouth of a drain line) in the fluid line cannot be detected.